1. Technical Field
The present invention relates to spindle motors utilizing dynamic pressure bearings, and in particular to low-profile, small-diameter spindle motors for spin-driving recording disks of small outside diameter, such as 1-inch.
2. Description of Related Art
Owing to advances in telecommunications technology and to increases in data volume, attempts to load hard-disk and other recording-disk drives, which had been utilized in conventional personal computers, into ultra-miniature information devices such as portable information terminals have begun.
Because the emphasis in these information devices is on compactness and lightness of weight, the dimension in the height direction that is allowed their recording-disk drives is being restricted to approximately 2 mm. Likewise, there has been a trend toward making the recording disks themselves diametrically smaller, and in recent years ultra-small-diameter hard disks one inch across have been put into practical use. Consequently, calls for miniaturizing and slimming-down, as well as for improving the rotational precision of, the drives that drive these recording-disks are increasingly on the rise.
Furthermore, the trend toward lower-priced information devices utilizing these recording-disk drives has been pronounced, which has raised demands for reduced costs in the spindle motors for recording-disk drives all the more.
Responding to such demands as noted above has led, as for example with the spindle motor disclosed in Japanese Pat. App. Pub. No. 2001-139971, to the utilization of dynamic-pressure bearings, which provide bearing support by inducing dynamic pressure in a fluid such as oil, instead of the ball bearings that up till now had principally been used for supporting rotation of the rotor onto which the recording disks are fitted. In the Japanese Pat. App. Pub. No. 2001-139971 instance, herringbone-patterned, dynamic-pressure-generating grooves formed on the circumferential periphery of a flange-shaped plate provided on the shaft constitute a radial bearing section of the dynamic-pressure bearings set out in the conventional spindle motor disclosed.
Meanwhile, herringbone-patterned, dynamic-pressure-generating grooves formed on both the upper and lower faces of the plate constitute a pair of thrust bearings therein.
Dynamic-pressure bearings of this sort make non-contacting support of the rotor possible, by virtue of which high rotational precision with low vibration and noise is readily gained. Furthermore, in contrast to ball bearings, with which if high bearing rigidity is to be gained there is no choice but to employ large-diameter balls, with dynamic-pressure bearings, the more minute the gap in which fluid is retained, the higher their rigidity tends to be. This is a characteristic that is ideal for miniaturizing and slimming-down spindle motors.
Nevertheless, because only an extremely thin layer of fluid is present on the bearing surfaces of the minute gaps in dynamic-pressure bearings, they demand high precision in the dimensions and surface smoothness of the bearing-constituent components. This is because lack of precision in the components would lead to bearing surface contact, impairing the rotational precision. For this reason keeping fabrication costs down would be difficult, and responding to demands for reduced costs would not be an easy matter, if numerous dynamic-pressure-generating areas are, as with the conventional spindle motor noted earlier, to be formed. Likewise, the difficulty in securing regions such as the circumferential surface of the shaft to function as bearings (regions that contribute to generation of dynamic pressure) if the spindle motor is to be miniaturized and made low-profile leads to concern over the bearing rigidity being impaired.
Thus, improvement in rotational precision, together with reduction in manufacturing cost, of a spindle motor applicable even to miniature, low-profile recording-disk drives has been desired.
Further, because portable information terminals operate on batteries, lessening power consumption of recording-disk drives that are utilized by such devices is a must.
An object of the present invention is to adapt a spindle motor utilizing dynamic-pressure bearings to miniature, low-profile recording-disk drives.
Another object is the realization of improvement in rotational precision, together with manufacturing cost reduction, in a spindle motor utilizing dynamic-pressure bearings.
A different object of the present invention is to effect a spindle motor of lesser electric power consumption.
To realize these objects a spindle motor under the present invention supports radial and thrust loads with a single dynamic-pressure bearing. Specifically, a conical part is furnished on the shaft, and the lateral face of the conical part is rendered a surface of a dynamic-pressure bearing. In a conically shaped hollow provided in the sleeve part of the motor the conical part is nested, which puts the lateral face of the conical part and the inner peripheral face of the conically shaped hollow in confrontation across a micro-gap, wherein oil is filled into the gap. Only a single dynamic-pressure bearing is formed along the conical lateral face.
Rendering the conical lateral face as the dynamic-pressure-bearing surface enables supporting loads with respect to both the radial and thrust directions by the one dynamic-pressure bearing. Likewise, the precision-working that dynamic-pressure surfaces require need be in one place only, which is advantageous in terms of lowering costs. Furthermore, miniaturizing and slimming-down the spindle motor are facilitated, compared to the situation in which the motor is built with both a radial bearing section and a thrust bearing section.
Further, rendering the dynamic-pressure bearing as only one reduces losses due to the oil""s viscous resistance. This accordingly reduces failures during rotation and enables the amount of power that the motor consumes to be controlled.
The dynamic-pressure generating grooves are preferably rendered in an unbalanced herringbone form, or as spiral grooves that impel the oil in a predetermined direction only. By thus rendering the groove geometry, pressure directed toward the bottom of the conical cavity is applied to the oil during rotation of the motor, raising the oil pressure near the bottom of the conical cavity and raising the bearing force in the thrust direction.
Other than bearing force due to dynamic pressure and bearing force due to pressurized oil, a magnetic biasing means is employed as a bearing force along the thrust direction. The magnetic biasing means acts in a direction counter to the other two bearing forces to control over-lift and stabilize support along the thrust direction. Further, the conical form of the dynamic-pressure-bearing surface stabilizes the thrust-directed support, whereby the radial-directed bearing support is also stabilized.
The opening of the conical hole is closed over by a disk-shaped cover in the middle of which, meanwhile, a hole through which the shaft passes is opened. The reverse face of the disk-shaped cover faces the basal surface of the conical part, and the radially outward area in the region sandwiched by these two surfaces is filled with oil. Meanwhile, with the area toward the center being filled with air, a gas-liquid interface is formed along the way in the region sandwiched by the two surfaces. Due to the surface tension of the oil, the gas-liquid interface forms a meniscus whose contour dips radially outward. Because the gas-liquid interface is pressed radially outward under centrifugal force during rotation of the motor, a stabilized sealing function is produced.
From the following detailed description in conjunction with the accompanying drawings, the foregoing and other objects, features, aspects and advantages of the present invention will become readily apparent to those skilled in the art.